# NTSB CEN16LA294: Bell 47G 2, N975BH, Oshkosh, WI, July 30, 2016 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 30, 2016, 15:05 local (20:05 UTC) - Place: Oshkosh, WI - Coordinates: 43.99139, -88.559722 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=43.9914&lon=-88.5597&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Defining event: [Approach-VFR pattern downwind: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed, report July 5, 2018 - Report: Approved by Office Director - NTSB office: Central Region - Parties: FAA - NTSB case key (mKey): 93717 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN16LA294 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/93717/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=93717 - Page: https://openairdocs.org/ntsb/CEN16LA294 ## Probable cause The loosening and separation of the throttle linkage nut, which resulted in a loss of throttle control and subsequent hard landing after autorotation. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine controls: power lever](https://openairdocs.org/ntsb-findings/01057603): Aircraft › Aircraft power plant · Inoperative (probable cause); cases with it: [Bell 47G-2, 1 case](https://openairdocs.org/ntsb-findings/01057603/cases.md?model=1181008), [All aircraft, 95 cases](https://openairdocs.org/ntsb-findings/01057603/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Approach-VFR pattern downwind: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [Bell 47G-2, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=1181008), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Autorotation: Engine shutdown](https://openairdocs.org/ntsb-events/140); cases with it: [Bell 47G-2, 1 case](https://openairdocs.org/ntsb-events/140/sequence.md?model=1181008), [All aircraft, 80 cases](https://openairdocs.org/ntsb-events/140/sequence.md) - [Autorotation: Hard landing](https://openairdocs.org/ntsb-events/092); cases with it: [Bell 47G-2, 3 cases](https://openairdocs.org/ntsb-events/092/sequence.md?model=1181008), [All aircraft, 2,102 cases](https://openairdocs.org/ntsb-events/092/sequence.md) ## Analysis The airline transport pilot maneuvered the helicopter on the downwind leg of the airport traffic pattern and attempted to reduce power for landing; however, the engine power remained excessively high. The pilot attempted to further reduce the engine power by turning off one magneto and applying carburetor heat, but the power remained too high to safely descend. The pilot then entered a sideslip, which allowed the helicopter to descend to about 100 ft above the runway. He turned the engine power off and autorotated to the ground. The helicopter landed hard in a tail-low attitude. The main rotor struck the tail and the tail rotor assembly separated from the helicopter. A postaccident examination found that the throttle linkage nut had loosened and separated from its fitting, causing the throttle to remain open. The helicopter's maintenance manual did not specify a torque value for the throttle linkage nut, and there were no maintenance procedures requiring the nut to be loosened or removed during overhaul. The pilot indicated that a complete overhaul of the helicopter was completed about 37 hours before the accident flight. ## Factual narrative On July 30, 2016, about 1500 central daylight time (CDT), a Bell 47 G2, N975BH, experienced a loss of engine power control during descent into Whittman Regional Airport (KOSH), Oshkosh, Wisconsin. The helicopter sustained substantial damage to the main rotor blades and tail. The airline transport-rated pilot and two passengers on-board were not injured. The helicopter was privately registered and operated by the Experimental Aircraft Association (EAA) under the provisions of 14 Code of Federal Regulations Part 136 as a commercial air tour flight. Visual meteorological conditions prevailed for the flight, and no flight plan was filed. The local flight originated at Pioneer Airport (WS17), Oshkosh, Wisconsin. The pilot explained that tour flights departed from Pioneer Airport (WS17), part of the Oshkosh Airport Complex, and flew over the EAA AirVenture Fly-In grounds then returned to the airport. Upon return to the airport, the pilot entered the downwind leg of the pattern and attempted to reduce power for landing. The power would only decrease to 3100rpm. The throttle was moved 'full travel' with no power change. The pilot explained that he wanted to maintain the collective to avoid over speeding the engine, but was unable to slow or descend. He switched to the right magneto and applied full carburetor heat to reduce the engine power; however, the power did not reduce enough to descend. After flying the traffic pattern "several times" attempting to descend, the pilot described putting the helicopter into a slip with the right pedal. He stated it was the only way to descend because when the pedals were in a neutral position the helicopter would climb with the engine still producing full power. He circled at the end of runway 9 to descend in altitude, getting to approximately 100 feet agl before shutting off the ignition and conducting a low altitude auto rotation. The helicopter impacted the ground "hard" on the back side of the skids, the main rotor blade struck the tail and the tail rotor assembly separated from the tail boom. The helicopter skidded to the left side of the runway and came to rest in the grass. The pilot stated there were no indications of a flight control problem in prior flights the day of the accident, or during the accident flight until returning to the airport at the completion of the tour. The pilot indicated a complete overhaul of the helicopter was completed 37.6 hours before the accident flight. An on-scene inspection of the helicopter by the FAA and NTSB personnel revealed the throttle linkage nut had loosened and separated from its fitting, this separation would result in complete loss of throttle control. The maintenance manual for the Bell 47 G-2 did not specify a torque value for this nut given there were no maintenance procedures requiring the nut to be loosened or removed. ## Aircraft - Registration: [N975BH](https://openairdocs.org/aircraft/N975BH), registered now, S/N 2242 (OpenAirDocs) - Reported make and model: BELL 47G 2 - Registry model: [Bell 47G-2](https://openairdocs.org/model/bell-47g-2) (registry code 1181008) (OpenAirDocs) - Category: Helicopter - Serial number: 2242 - Year built: 1959 - Airframe hours: 6866.1 - Engines: Lycoming VO-435 260 horsepower reciprocating - Damage: Substantial damage - Flight: Other work use, Part 91 - Operator: Experimental Aircraft Association - Registered owner: Matthew L Anderson - Airworthiness certificate: Standard, Normal - Last inspection: Annual, June 23, 2015 - Departed: OSH, Oshkosh, WI - Destination: OSH, Oshkosh, WI - Airport: OSH, Wittman Rgnl, runway 09, 6,179 × 150 ft, concrete ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 56; injuries: none; airline transport, commercial, flight engineer; airplane ratings: multi-engine land, single-engine land, single-engine sea; instrument ratings: airplane; medical: class 1, with waivers/limitations; last flight review July 18, 2016; seat: left; restraint: 4-point; flight hours: 25,000 total, 970 in this make and model, 11,000 as pilot in command, 32 in the last 90 days, 27 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Observed at: KOSH ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 20160730012699A](https://openairdocs.org/incident/20160730012699A), Jul 30, 2016: Bell 47G-2, Oshkosh, WI, Substantial damage. During level flight, engine throttle control cable came apart causing throttle to be stuck at 25'' manifold pressure. Pilot was unable to decend without… ## Docket (2 files) The files NTSB released with the investigation on December 26, 2017, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=93717. 976 KB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 402 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40459079&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Photos (item 2, .PDF, 4 photos, 574 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40459080&FileExtension=.PDF&FileName=Photos-Master.PDF From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.